104 healthy women who had been attempting to become pregnant for three months were interviewed about their use of caffeinated beverages, alcohol, and cigarettes. In their subsequent cycles, women who consumed more than the equivalent of one cup of coffee per day were half as likely to become pregnant, per cycle, as women who drank less. A dose-response effect was present.
PIP: Fecundability of 104 healthy women attempting to become pregnant was halved by consumption of the equivalent of 1 cup of brewed coffee or more daily. 104 women who had not conceived after 3 months during a larger study of early pregnancy loss were interviewed about consumption of coffee, tea and caffeinated beverages. Those consuming over 3150 mg caffeine per month, the median, were considered in the high consumption group, and those consuming less the low group. Fecundability, the probability of becoming clinically pregnant in a given menstrual cycle, when expressed as a ratio, averaged 0.59 over the 3rd to 8th cycle, and 0.53 after 6 more months in the high consumption group. Multivariate analysis, controlling for age, frequency of intercourse, and age at menarche, found no effect for these variables, nor for smoking, vitamins, analgesics, alcohol, marijuana, weight, height, or husband's caffeine consumption. When the data were divided into 5 dose levels, there was a dose-response effect: fecundability of the highest consumption group fell to 26% of that of the lowest group. When the data were treated by the life table approach, 6% of the women were still not pregnant in the low consumption group by cycle 13, compared to 28% in the high consumption group, a relative risk of 4.7 (p0.005). The mechanism of action of caffeine on fecundability is unknown.